1. Field of the Invention
The present invention relates generally to thrust washers and thrust bearings and particularly concerns thrust washers and thrust bearings provided with stamped resilient projections serving as locating and retaining springs.
2. Description of Prior Developments
Thrust washers and thrust bearings have previously been formed with one or more locating members such as tabs, lugs and tangs. These locating members are provided for preventing the washers and bearings from rotating during operation as well as for orienting and properly locating the washers and bearings in an assembly such as a transmission housing or engine crankcase. Thrust bearings of this general type are disclosed in U.S. Pat. Nos. 4,795,220 and 4,770,547.
With some conventional thrust bearing designs, the washer-shaped bearing can become dislodged if the component upon which it is seated is inverted, turned upside down or otherwise manipulated during various assembly operations. To correct this problem, grease or a similar tacky substance has been applied to the interface between the bearing and its support surface to hold the bearing in place during assembly.
Another approach to securing thrust bearings in place during assembly is to form a mechanical non-yielding fit between the locating tangs provided on the bearings and the bearing housing mounting surfaces, recesses or pockets on or within which the tangs are seated. This is the approach followed in U.S. Pat. No. 4,770,547 noted above. This approach can in some cases require costly machining of the bearing support housing to provide the required pockets or recesses for the locating tangs.
Moreover, in those cases where the pockets or seats for the locating tangs are cast into the bearing housing, excessive and often unacceptable tolerances are experienced between the tangs and the as-cast mounting surfaces. This condition can result in inadequate retention forces or excessive interference between the bearing tangs and bearing housing mounting surfaces. Inadequate retention forces cause the bearing to become easily dislodged from its housing, while excessive interference can distort the bearing and/or prevent proper seating of the bearing in its housing.
As seen in FIG. 1 as well as in U.S. Pat. 4,770,547, some locating tabs have been bent through an angle of about 90.degree.. Although these tabs will hold the bearing in place in some cases, such tabs do not provide a resilient or biased retention force required for robotic assembly operations. Some designs increase the bend angle to greater than 90.degree. so that the tab is placed in tension as it engages the side wall of its mounting recess and is bent back toward a 90.degree. bend as seen in FIG. 2. The amount of bend past 90.degree. is limited by the ability to remove the tab from its forming die after bending. A particular drawback to this design is that it can result in the sharp corners of the free end of the tab digging into the bearing mounting surface and obstructing installation of the bearing.
Accordingly, a need exists for a thrust bearing having a self-locking tang which positively and resiliently retains the bearing within its housing, yet which is easily removed from its die during stamping and forming.
Another need exists for a thrust washer which does not require any secondary machining on itself or on its mounting surface or housing so that it may be directly mounted to an as-cast surface or as-cast housing.
Still another need exists for a thrust bearing which does not require grease or a similar tacky substance to retain the thrust bearing on its mounting surface.
Yet another need exists for a thrust bearing having resilient mounting tangs which accommodate significant assembly tolerances yet which are easily insertable within their mounting recesses without requiring excessive insertion force.
Another need exists for a thrust bearing which facilitates its assembly to a bearing housing by providing a self-centering profile which guides the thrust bearing with a compressive resilient wedging action into its proper seating position without digging or plowing into the bearing mounting surface during installation.